The present invention relates generally to an implantable stimulation lead for use with an implantable pulse generator such as a cardiac pacemaker and, more specifically to such an implantable stimulation lead with the capability of selectively anchoring an electrically active helix electrode at a desired site when the lead is fixated in the heart, then withdrawing the electrode from the site.
Currently, known extendable/retractable screw-in implantable stimulation leads have an electrically active helix electrode. The helix electrode is electrically active and is capable of extension and retraction from the header by being directly connected to the connector pin/distal coil subassembly. Turning of the connector pin results in the extension or retraction of the helix electrode from the header. In order for the helix to be extended or retracted, a thread/screw mechanism is required. The helix electrode is used as a threaded screw which turns against a thread post in the header. As the helix rotates, by turning of the connector pin, it engages the thread post, which in turn drives the helix into and out of the header. This thread/screw mechanism works smoothly when the helix electrode is straight and undamaged. However, the helix is susceptible to deformation due to its xe2x80x9cdelicatexe2x80x9d strength and mishandling during assembly processes. A deformed or damaged helix will not only cause undesirable xe2x80x9cstickyxe2x80x9d or xe2x80x9cjumpyxe2x80x9d helix movement during the extension/retraction operation, but it may also disable the thread/screw mechanism. In addition, the thread/screw mechanism may be jammed by heart tissues that may become trapped inside the header.
Typical of the known prior art are commonly assigned U.S. Pat. Nos. 5,447,533 to Vachon et al.; 5,531,780 to Vachon; 5,649,975 to Lindegren et al.; and 5,833,715 to Vachon et al., each of which discloses an active helix electrode system employed with an implantable stimulation lead.
It was in light of the foregoing that the present invention was conceived and has now been reduced to practice.
An implantable endocardial lead for use with a cardiac stimulation device includes an electrical conductor whose proximal end is coupled to an electrical connector. An active fixation electrode is coupled to the distal end of the conductor, being movable between a retracted position fully within the lead and an extended position advanced beyond the distal end of the lead for effecting penetration into the myocardial tissue. The lead includes an electrically active housing including a tubular end region extending to a terminal rim at the distal end of the lead and an electrical conductor within the lead extends between proximal and distal ends. The active fixation electrode is located within and spaced from the electrically active housing and includes an electrically active helix coaxial with the endocardial lead coupled to the distal end of the electrical conductor and movable between a retracted position fully within the housing and an extended position advanced beyond the terminal rim of the housing for effecting penetration into the myocardial tissue. A guide system located proximally of the active fixation electrode serves to rotate the electrically active helix about the longitudinal axis as the helix is moved between the retracted and extended positions.
In the new thread/screw mechanism for the extendable/retractable helix of a screw-in lead, contrasting with the prior art, the helix electrode is no longer used as part of the thread/screw mechanism. In one embodiment, the thread/screw mechanism is relocated to the back of the header. A spiral groove creating the thread is integrated onto the header. A thread post is mounted onto the stopper. The combination of the stopper and the header provides the thread/screw mechanism for helix extension/retraction. The spiral groove of the header and the thread post of the stopper are both more robust and stronger than the combination helix electrode and header thread post. Potential helix jamming problems due to the heart tissue entrapment are also minimized since the thread/screw mechanism is located in the back end of the header where it is isolated from tissue. The functional improvements resulting from this new design provides a reliable thread/screw mechanism.
Other and further features, advantages, and benefits will become apparent in the following description taken in conjunction with the following drawings. The accompanying drawings illustrate exemplary embodiments together with the description. Like numerals refer to like parts throughout the disclosure.